The first four Antares launch attempts were successful. During the fifth launch on October 28, 2014, the rocket failed catastrophically, and the vehicle and payload were destroyed.[15] The failure was traced to a fault in the first stage engines. After completion of a redesign program, the rocket had a successful return to flight on October 17, 2016, delivering cargo to the ISS.

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The NASA COTS award was for US$171 million and Orbital Sciences expected to invest an additional $150 million, split between $130 million for the booster and $20 million for the spacecraft.[16] A Commercial Resupply Service contract of $1.9 billion for 8 flights was awarded in 2008.[17] As of April 2012, development costs were estimated at $472 million.[2]

On December 10, 2009, Alliant Techsystems Inc. (ATK) test fired their Castor 30 motor for use as the second stage of the Antares rocket.[22] In March 2010 Orbital Sciences and Aerojet completed test firings of the NK-33 engines.[23] On February 22, 2013, a hot fire test was successfully performed, the entire first stage being erected on the pad and held down while the engines fired for 29 seconds.[21]

The first stage of Antares burns RP-1 (kerosene) and liquid oxygen (LOX). As Orbital had little experience with large liquid stages and LOX propellant, the first stage core was designed and is manufactured in Ukraine by Yuzhnoye SDO[16] and includes propellant tanks, pressurization tanks, valves, sensors, feed lines, tubing, wiring and other associated hardware.[24] Like the Zenit—also manufactured by Yuzhnoye—the Antares vehicle has a diameter of 3.9 m (150 in) with a matching 3.9 m payload fairing.[7]

The Antares 100-series first stage was powered by two AerojetAJ26 engines. These began as KuznetsovNK-33 engines built in the Soviet Union in the late 1960s and early 1970s, 43 of which were purchased by Aerojet in the 1990s. 20 of these were refurbished into AJ26 engines for Antares.[25] Modifications included equipping the engines for gimballing, adding US electronics, and qualifying the engines to fire for twice as long as designed and to operate at 108% of their original thrust.[4][23] Together they produced 3,265 kilonewtons (734,000 lbf) of thrust at sea level and 3,630 kN (816,100 lbf) in vacuum.[9]

Following the catastrophic failure of an AJ26 during testing at Stennis Space Center in May 2014 and the Orb-3 launch failure in October 2014, likely caused by an engine turbopump,[26] the Antares 100-series was retired.

Due to concerns over corrosion, aging, and the limited supply of AJ26 engines, Orbital had selected new first stage engines. The new engines were planned to debut in 2017 and allow Orbital to bid on a second major long-term contract for cargo resupply of the ISS. Less than one month after the loss of the Antares rocket in October 2014, Orbital announced that it would no longer fly Antares with AJ26 engines,[27] and the first flight of Antares with new first stage engines would be moved up to 2016.[23] In December 2014 Orbital Sciences announced that the Russian RD-181—a modified version of the RD-191—would replace the AJ26 on the Antares 200-series.[28][29] The first flight of the re-engined Antares 230 configuration was October 17, 2016 carrying the Cygnus CRS OA-5 cargo to the ISS.

The Antares 200 and 200+ first stages are powered by two RD-181 engines, which provide 440 kilonewtons (100,000 lbf) more thrust than the dual AJ26 engines used on the Antares 100. Orbital adapted the existing core stage to accommodate the increased performance in the 200 Series, allowing Antares to deliver up to 6,500 kg (14,300 lb) to low Earth orbit.[8] The surplus performance of the Antares 200-series will allow Orbital to fulfill its ISS resupply contract in only four additional flights, rather than the five that would have been required with the Antares 100-series.[30][31][32]

While the 200 series uses the RD-181 by adapting the originally ordered 100 Series stages (Yuzhnoye SDO/Yuzhmash, Zenit derived),[33] it requires under-throttling the RD-181 engines, which reduces performance.[31]

Kurt Eberly, Vice President and Antares Program Manager for Orbital ATK, outlined the Antares upgrades for the NASA CRS-2 (Commercial Resupply Services 2) contract, in a May 2018 interview. OA-12, scheduled for late 2019, will be the first NASA CRS-2 mission to ISS. Planned upgrades to the Antares 230 variant will not, as previously suggested, be referred to as Antares 300 but instead will be the Antares 230+. Eberly stated the most significant upgrades would be structural changes to the intertank bay (between the LO2 and RP-1 tanks) and the forward bay (forward of the LO2). Additionally, the company is working on trajectory improvements via a "load-release autopilot" that will provide greater mass to orbit capability.[34]

The second stage is an Orbital ATK Castor 30-series solid-fuel rocket, developed as a derivative of the Castor 120 solid motor used as Minotaur-C's first stage.[35] The first two flights of Antares used a Castor 30A, which was replaced by the enhanced Castor 30B for subsequent flights. The Castor 30B produces 293.4 kN (65,960 lbf) average and 395.7 kN (88,960 lbf) maximum thrust, and uses electromechanicalthrust vector control.[9] For increased performance, the larger Castor 30XL is available[33] and will be used on ISS resupply flights to allow Antares to carry the Enhanced Cygnus.[9][36][37]

The Castor 30XL upper stage for Antares 230+ is being optimized for the CRS-2 contract. The initial design of the Castor 30XL was conservatively built, and after gaining flight experience it was determined that the structural component of the motor case could be lightened.[34]

Antares offers three optional third stages: the Bi-Propellant Third Stage (BTS), a Star 48-based third stage and an Orion 38 motor. BTS is derived from Orbital Sciences' GEOStar spacecraft bus and uses nitrogen tetroxide and hydrazine for propellant; it is intended to precisely place payloads into their final orbits.[7] The Star 48-based stage uses a Star 48BV solid rocket motor and would be used for higher energy orbits.[7] The Orion 38 is used on the Minotaur and Pegasus rockets as an upper stage.[38]

On January 14, 2016, NASA awarded three cargo contracts via CRS2. Orbital ATK's Cygnus was one of these contracts.[40]

According to Mark Pieczynski, Orbital ATK Vice President, Flight Systems Group, “A further improved version [of Antares for CRS2 contract] is in development which will include: Stage 1 core updates including structural reinforcements and optimization to accommodate increased loads.

“(Also) certain refinements to the RD-181 engines and CASTOR 30XL motor; and Payload accommodations improvements including a ‘pop-top’ feature incorporated in the fairing to allow late Cygnus cargo load and optimized fairing adapter structure.”

Previously, it was understood that these planned upgrades from the Antares 230 series would create a vehicle known as the Antares 300 series. However, when asked specifically about Antares 300 series development, Mr. Pieczynski stated that Orbital ATK has “not determined to call the upgrades, we are working on, a 300 series. This is still TBD.”[41] In May 2018, Antares program manager Kurt Eberly indicated that the upgrades will be referred to as Antares 230+.[34]

The first two test flights used a Castor 30A second stage. All subsequent flights will use either a Castor 30B or Castor 30XL. The rocket's configuration is indicated by a three-digit number and a possible "+" suffix, the first number representing the first stage, the second the type of second stage, and the third the type of third stage.[36] A plus sign added as suffix (fourth position) signifies performance upgrades to the Antares 230 variant.

Prior to the launch, a 27-second test firing of the rocket's AJ26 engines was conducted successfully on February 22, 2013, following an attempt on February 13 which was abandoned before ignition.[21]

A-ONE used the Antares 110 configuration, with a Castor 30A second stage and no third stage. The launch took place from Pad 0A of the Mid-Atlantic Regional Spaceport on Wallops Island, Virginia. LP-0A was a former Conestoga launch complex which had only been used once before, in 1995, for the Conestoga's only orbital launch attempt.[11] Antares became the largest — and first — liquid-fuelled rocket to fly from Wallops Island, as well as the largest rocket launched by Orbital Sciences.[42]

The first attempt to launch the rocket, on April 17, 2013, was scrubbed after an umbilical detached from the rocket's second stage, and a second attempt on April 20 was scrubbed due to high altitude winds.[46] At the third attempt on April 21, the rocket lifted off at the beginning of its launch window. The launch window for all three attempts was three hours beginning at 21:00 UTC (17:00 EDT), shortening to two hours at the start of the terminal count, and ten minutes later[clarification needed] in the count.[11][47]

On October 28, 2014, the attempted launch of an Antares carrying a Cygnus cargo spacecraft on the Orb-3 resupply mission failed catastrophically six seconds after liftoff from Mid-Atlantic Regional Spaceport at Wallops Flight Facility, Virginia.[48] An explosion occurred in the thrust section just as the vehicle cleared the tower, and it fell back down onto the pad. The Range Safety officer sent the destruct command just before impact.[15][49] There were no injuries.[50] Orbital Sciences reported that Launch Pad 0A "escaped significant damage,"[49] though initial estimates for repairs were in the $20 million range.[51] Orbital Sciences formed an anomaly investigation board to investigate the cause of the incident. They traced it to a failure of the first stage LOX turbopump, but could not find a specific cause. However, the refurbished NK-33 engines, originally manufactured over 40 years earlier and stored for decades, were suspected as having leaks, corrosion, or manufacturing defects that had not been detected.[52] The NASA Accident Investigation Report was more direct in its failure assessment.[53] On October 6, 2015, almost one year after the accident, Pad 0A was restored to use. Total repair costs were about $15 million.[54]

Following the failure, Orbital sought to purchase launch services for its Cygnus spacecraft in order to satisfy its cargo contract with NASA,[27] and on December 9, 2014, Orbital announced that at least one, and possibly two, Cygnus flights would be launched on Atlas V rockets from Cape Canaveral Air Force Station.[55] As it happened, Cygnus OA-4 and OA-6 were launched with an Atlas V and the Antares 230 performed its maiden flight with Cygnus OA-5 in October 2016. One further mission was launched aboard an Atlas in April 2017 (OA-7), fulfilling Orbital's contractual obligations towards NASA. It was followed by the Antares 230 in regular service with OA-8E in November 2017, with three further missions scheduled on their extended contract.

Orbital Sciences COTS demonstration flight. First Antares mission with a real Cygnus capsule, first mission to rendezvous and berth with the International Space Station, second launch of Antares. The rendezvous maneuver was delayed due to a computer data link problem,[59] but the issue was resolved and berthing followed shortly thereafter.[60][61]

Spacecraft carried ISS hardware, crew supplies, and scientific payloads, including the Cold Atom Lab and the Biomolecule Extraction and Sequencing Technology experiment.[79] The Cygnus also demonstrated boosting the station’s orbital velocity for the first time, by 0.06 meters per second.[80]

Note: Cygnus CRS OA-4, the first Enhanced Cygnus mission, and OA-6 were propelled by Atlas V 401 launch vehicles while the new Antares 230 was in its final stages of development. Cygnus CRS OA-7 was also switched to an Atlas V and launched on April 18, 2017.

^ ab"Orbital's Cygnus – on a SpaceX Falcon 9?". spaceflightinsider.com. November 24, 2014. Retrieved November 28, 2014. Orbital has announced that it is planning to use another engine on Antares and that it will likely not use any more of the 40-year-old AJ-26 engines on the rocket’s next flight – which Orbital hopes to conduct in 2016.